We assume that both GN 1 and GN 2 are equipped with an omni-directional single antenna. The RIS is fitted with a uniform linear array (ULA) of \(M\)  reflective elements, each of which can be manipulated by an embedded development board, such as Raspberry Pi 4, mounted on the UAV. Since the UAV and the RIS are assembled compactly, we assume that their 3D coordinates are identical, causing negligible performance loss due to high flying altitude of the UAV [1]}. We denote \(\Theta [n]=\operatorname{diag}\left\lbrace e^{j \theta _{1}[n]}, e^{j \theta _{2}[n]}, \cdots , e^{j \theta _{M}[n]}\right\rbrace \)  as the
diagonal phase-shift matrix of the RIS in the \(n\) th time slot, where \(\theta _{m}[n] \in [0,2 \pi ), m \in \mathcal {M}=\lbrace 1, \cdots , M\rbrace \)  is the \(m\) th phase shift of the RIS in the \(n\) th time slot.
